Content uploaded by James G Gehling
Author content
All content in this area was uploaded by James G Gehling on Dec 08, 2015
Content may be subject to copyright.
The case for the Ediacaran fossil roots to the Metazoan Tree
Abstract
The first challenge to the traditional interpretation of the Late Proterozoic Ediacara fossils came with a paper by A. Seilacher (1984, 1989) which not only proposed that Ediacaran organisms became extinct before the Cambrian, but that they represented a previously unrecognized kingdom of structurally unique multicellular organisms: the Vendozoa. This new model is based on a number of uncontested generalizations about size, shape, lifestyle and preservation, that have persisted in the literature. Many of these assumptions are now shown to be misconceptions, as a consequence of newly discovered material in Australia, Canada and the USSR, revealing a more diverse fossil assemblage and suggesting that the organisms were dominantly benthic. The interpretation of this biota in phylogenetic terms, is vindicated by the realization of strong links between some Ediacaran and Cambrian organisms. -from Author
... The smallest distinguishable specimens of Dickinsonia are 1-2 mm long (Ivantsov & Zakrevskaya 2022). The average length of their body is a few centimetres, although there are known specimens that reach 1 metre in length (Gehling 1991;Jenkins 1992;Gehling et al. 2005) and possibly even bigger ones, reconstructed from fragments (Jenkins 1996). The length of the largest White Sea specimen of D. tenuis, which is not completely visible on the surface of the bearing layer, exceeds 55 cm. ...
... The structure as a whole can stand out rather sharply in the relief of imprints (Fig. 3a, c), but it disappears at a high degree of tissue decomposition (Fig. 1c). Apparently, it represented some kind of a band that lay inside the body of Dickinsonia (Wade 1972;Runnegar 1982;;Gehling 1991;Jenkins 1992;Evans et al. 2019а;Ivantsov & Zakrevskaya 2022). ...
... The nature of the linear axial structure of Dickinsonia is discussed here. It is hypothesised that the food-filled gut could have been preserved in this form (Wade 1972;Runnegar 1982;Gehling 1991;Jenkins 1992), but it is also believed that it was a mechanical artefact that arose during the process of fossilisation (Brasier & Antcliffe 2008) or that the axial structure, 'midline', was like a dense membrane to which the transverse elements were attached (Gehling et al. 2005;Evans et al. 2017). In one of their papers, Evans et al. (2019a) suggest that the 'midline' was filled with fluid and acted as a hydrostatic skeleton during the work of various muscles of Dickinsonia. ...
Materials collected on the territory of the southeastern White Sea area, including diversely preserved body imprints, combined body-trace fossils, specimens with signs of intravital damage and regeneration, and extended ontogenetic series, make it possible to significantly widen the data on the body plan and biology of Dickinsonia, the oldest known mobile animal, included in the Late Pre-cambrian taxon of high rank, Proarticulata. A number of reconstructed anatomical features were added to the obvious directly observed features of Dickinsonia, such as a consistent body shape lacking lateral appendages and temporary outgrowths, transverse differentiation, and anterior-posterior polarity. These reconstructed features include dorsoventral polarity, ciliated mucus-secreting epithelium underlain by a basal lamina, two rows of blind food-gathering pockets, absence of a through-gut, nervous system of diffusive type, axial support band and muscle fibres. Such a set of features indicates the affinity of Dickinsonia and Proarticulata as a whole (the only known Ediacaran Metazoa) to Urbilateria, a hypothetical ancestor of bilaterally symmetrical animals.
... Microfossils, microbialites (stromatolites, leiolites, thrombolites, dendrolites) and geochemical data are widely used to study the oldest traces of life (Schopf, 1999;Watanabe et al., 2000;Altermann & Kazmierczak, 2003). Recently, another taphonomic window has been developed based on actualistic comparisons with structures developed by the interaction of microbial mats, siliciclastic sediments and environmental conditions (Gehling, 1991;Eriksson et al., 2007). The combination of microbial mat activity (growth, bioprecipitation, and decay) and environmental conditions often can result in the formation of several biomat-related structures in siliciclastic sediments that can be preserved in the geological record. ...
... The combination of microbial mat activity (growth, bioprecipitation, and decay) and environmental conditions often can result in the formation of several biomat-related structures in siliciclastic sediments that can be preserved in the geological record. These are now collectively known as microbially induced sedimentary structures (MISS) Noffke, 2009;Sarkar et al., 2014;Davies et al., 2016;Gehling, 1991;Aref et al., 2020;Seilacher et al., 1994;Seilacher, 1999;Noffke, 2021). ...
The Eastern Anti-Atlas of Morocco hosts an early Ediacaran turbiditic series (Saghro Group) (630–600 Ma) unconformably overlain by thick late Ediacaran (580–550 Ma) terrestrial volcano-clastic formations (Ouarzazate Supergroup), with thin and geographically limited paralic shallow marine sedimentary rocks.
This paper presents the first description of structures related to the former presence of extensive microbial mats developed in marine, fluvial, and lacustrine environments during the Ediacaran in the Eastern Anti-Atlas. These microbially induced sedimentary structures (MISS) are largely found in well-laminated fine- to coarse-grained sandstone and sandy-carbonate. They also cover vast bedding planes and occur in almost all sedimentary successions. MISS types include: gas domes, wrinkle structures, reticulate patterns, overflips and roll-ups, multidirectional linear ridges, sand cracks and biolaminated deposits. Based on morphology and petrographic macro and microfabrics, these microbially induced structures are very similar to those of modern photosynthetic cyanobacteria mats. Together with previously reported stromatolites, these newly reported microbial mat structures could have played an important ecological role in stabilizing siliciclastic sediments, as well as sustaining localized zones of high oxygen production in the Ediacaran marine and terrestrial paleoenvironments of the Anti-Atlas. The widespread geographic distribution and consistent occurrence of microbially induced sedimentary structures (MISS) in fluvial and lacustrine sediments present compelling paleontological evidence supporting the extensive greening of the land surface during the late Precambrian period.
... The Precambrian life forms discovered, notably the Ediacara fauna, have been interpreted as several distinct members of the Metazoa crown group (Gehling, 1991;Dzik, 2003;Waggoner, 2003); some organisms have been interpreted as microbial colonies, or even lichens (Peterson et al., 2003;MacGabhann, 2007;Retallack, 2012Retallack, , 2013. It has also been proposed the denomination of vendobionts for these organisms which could constitute a separate phylum, today without descendants (Seilacher, 1989(Seilacher, , 1992Buss et Seilacher, 1994;Xiao et Laflamme, 2009;Dunn et al., 2018). ...
... There are various interpretations as to the nature of these fossils; some researchers (Gehling, 1991) believe that these organisms could be the oldest sponges, but this theory is not accepted by most scientists. Another hypothesis (Sepkoski et al., 2002) sees Rugoconites as a representative of cnidarians, such as a jellyfish; Ivantstov and Fedonkin (2003) hypothesized that it must be a representative of trilobozoans, a mysterious group of triradiate-symmetric bodies of uncertain affinity. ...
... Though it is relatively common in fossiliferous Ediacaran rocks of South Australia, Aulozoon evaded formal description until recently due to a long history of contradicting identifications as various forms of back stuffed or mucus lined burrows (Glaessner, 1969;Jenkins, 1995;Seilacher et al., 2003;Seilacher, 2007), and as fungal rhizomorphs (Retallack, 2007(Retallack, , 2013. Several studies have interpreted Aulozoon as a metazoangrade body fossil (Gehling, 1991;Fedonkin and Runnegar, 1992;Runnegar, 1994;Ivantsov, 2011;Droser et al., 2006), which was confirmed in the formal description of Aulozoon by Gehling and Runnegar (2022). ...
... Nevertheless, these efforts were overwhelmingly focused on the subsequent 'explosion' of animal phyla in the early Cambrian, rather than the disappearance of Ediacaran soft-bodied organisms below the boundary. This is perhaps not surprising given that, prior to propositions by Seilacher (1984Seilacher ( , 1985Seilacher ( , 1989Seilacher ( , 1992, the Ediacara biota were overwhelmingly interpreted as belonging to extant metazoan groups (e.g., Glaessner, 1984;Gehling, 1991). As such, the fossil record of the E-C transition could be satisfactorily explained as the result of taphonomic biases towards the preservation of biomineral shells, Figure 1. ...
Since the 1980s, the existence of one or more extinction events in the late Ediacaran has been the subject of debate. Discussion surrounding these events has intensified in the last decade, in concert with efforts to understand drivers of global change over the Ediacaran–Cambrian transition and the appearance of the more modern-looking Phanerozoic biosphere. In this paper we review the history of thought and work surrounding late Ediacaran extinctions, with a particular focus on the last 5 years of paleontological, geochemical, and geochronological research. We consider the extent to which key questions have been answered, and pose new questions which will help to characterize drivers of environmental and biotic change. A key challenge for future work will be the calculation of extinction intensities that account for limited sampling, the duration of Ediacaran ‘assemblage’ zones, and the preponderance of taxa restricted to a single ‘assemblage’; without these data, the extent to which Ediacaran bioevents represent genuine mass extinctions comparable to the ‘Big 5’ extinctions of the Phanerozoic remains to be rigorously tested. Lastly, we propose a revised model for drivers of late Ediacaran extinction pulses that builds off recent data and growing consensus within the field. This model is speculative, but does frame testable hypotheses that can be targeted in the next decade of work.
... THE Ediacaran biota is the oldest and distinct group of macroscopic, morphologically complex eukaryotic organisms that flourished in the late Ediacaran period 1,2 . They are mainly soft-bodied organisms with unusual body plans 3 and have been historically interpreted as the evolutionary precursors of Cambrian organisms or animals, including annelids, cnidarians, arthropods and echinoderms 4,5 . Among these, many Ediacaran taxa have tri-radial symmetry or body plan 2,3 and occur as three elevated, equal-spaced features or forms such as lobes, bumps, ridges or canals, as well as some elements of threefold symmetry arranged or bound in a peripheral ring 2,6,7 . ...
Here we describe the Tribrachidium and Albumares
Ediacaran organisms belonging to phylum Trilobozoa
in the Sonia Sandstone of Marwar Supergroup, western
India. Between the two Ediacaran genera, Albumares
brunsae was the first to be discovered in India, while
Tribrachidium heraldicum was the first record from the
Marwar Supergroup. T. heraldicum is soft-bodied, dis�coidal or disc-shaped (in plane view) and slightly coni�cal-shaped (when found with up to 2 mm vertical relief)
with three elevated lobes (arms) or ridges bounded by
a well-defined peripheral ring. A. brunsae is soft-bodied,
flattened, low-relief, circular to sub-circular and with
a tri-lobed (three elevated arms/rays) shield having
branching rays that radiate outward from the centre to
the outer edge of the peripheral ring. Both Ediacaran
taxa occur here as convex or positive reliefs with tri�radial symmetry on medium to fine-grained sandstone
bedding planes in the Sursagar area and show the Flin�ders Ranges style of preservation.
Keywords: Albumares, Ediacaran organisms, sandstone,
Tribrachidium, trilobozoan
... THE Ediacaran biota is the oldest and distinct group of macroscopic, morphologically complex eukaryotic organisms that flourished in the late Ediacaran period 1,2 . They are mainly soft-bodied organisms with unusual body plans 3 and have been historically interpreted as the evolutionary precursors of Cambrian organisms or animals, including annelids, cnidarians, arthropods and echinoderms 4,5 . Among these, many Ediacaran taxa have tri-radial symmetry or body plan 2,3 and occur as three elevated, equal-spaced features or forms such as lobes, bumps, ridges or canals, as well as some elements of threefold symmetry arranged or bound in a peripheral ring 2,6,7 . ...
Here we describe the Tribrachidium and Albumares Ediacaran organisms belonging to phylum Trilobozoa in the Sonia Sandstone of Marwar Supergroup, western India. Between the two Ediacaran genera, Albumares brunsae was the first to be discovered in India, while Tribrachidium heraldicum was the first record from the Marwar Supergroup. T. heraldicum is soft-bodied, dis-coidal or disc-shaped (in plane view) and slightly conical shaped (when found with up to 2 mm vertical relief) with three elevated lobes (arms) or ridges bounded by a well-defined peripheral ring. A. brunsae is soft-bodied, flattened, low-relief, circular to sub-circular and with a tri-lobed (three elevated arms/rays) shield having branching rays that radiate outward from the centre to the outer edge of the peripheral ring. Both Ediacaran taxa occur here as convex or positive reliefs with tri-radial symmetry on medium to fine-grained sandstone bedding planes in the Sursagar area and show the Flin-ders Ranges style of preservation.
... Charnia and other rangeomorphs have been variously interpreted as pennatulacean cnidarians (Glaessner, 1959(Glaessner, . 1984Glaessner and Wade, 1966;Gehling, 1991), lichens (Retallack, 1994), fungi (Peterson et al., 2003), members of the extinct kingdom Vendobionta (Seilacher, 1992), or members within the total-group Metazoa (e.g., Xiao and Laflamme, 2009;Dunn et al., 2018;Butterfield, 2022). Although Charnia and modern sea pens both possess a similar leaf-like shape, ontogenetic analysis reveals that Charnia and modern sea pens may have opposite growth polarities Brasier, 2007, 2008). ...
The terminal Ediacaran Shibantan biota (~550–543 Ma) from the Dengying Formation in the Yangtze Gorges area of South China represents one of the rare examples of carbonate-hosted Ediacara-type macrofossil assemblages. In addition to the numerically dominant taxa—the non-biomineralizing tubular fossil Wutubus and discoidal fossils Aspidella and Hiemalora , the Shibantan biota also bears a moderate diversity of frondose fossils, including Pteridinium , Rangea , Arborea , and Charnia . In this paper, we report two species of the rangeomorph genus Charnia , including the type species Charnia masoni Ford, 1958 emend. and Charnia gracilis new species, from the Shibantan biota. Most of the Shibantan Charnia specimens preserve only the petalodium, with a few bearing the holdfast and stem. Despite overall architectural similarities to other Charnia species, the Shibantan specimens of Charnia gracilis n. sp. are distinct in their relatively straight, slender, and more acutely angled first-order branches. They also show evidence that may support a two-stage growth model and a epibenthic sessile lifestyle. Charnia fossils described herein represent one of the youngest occurrences of this genus and extend its paleogeographic and stratigraphic distributions. Our discovery also highlights the notable diversity of the Shibantan biota, which contains examples of a wide range of Ediacaran morphogroups.
UUID: http://zoobank.org/837216cd-4a4a-4e13-89e2-ee354ba48a4c
The recognition of fossiliferous horizons both below and above the classical Ediacara levels of the Flinders Ranges, South Australia, significantly expands the potential of this candidate World Heritage succession. Here we document a small window into the biology and taphonomy of the late Ediacaran seafloor within the new Nilpena Sandstone Member of the Rawnsley Quartzite in Bathtub Gorge, northern Heysen Range. A 1 m ² slab extracted from the gorge, now on permanent display at the South Australian Museum, has a death assemblage dominated by the erniettomorph Phyllozoon hanseni Jenkins and Gehling 1978 and a newly named macroscopic tubular body fossil – Aulozoon soliorum gen. et sp. nov. – on its fine sandstone bed sole. The orientations and juxtaposition of these taxa suggest overprinting of an in situ benthic Phyllozoon community by sand-filled tubes of Aulozoon carried in by a storm wave-base surge. Phyllozoon hanseni is a widespread species that is restricted to the Nilpena Sandstone Member of the Rawnsley Quartzite, whereas Dickinsonia costata ranges from the underlying Ediacara Sandstone Member into the Nilpena Sandstone Member. Fundamental differences in the ways these two vendobiont taxa are constructed and preserved may provide insights into their biology and phylogenetic affinities. In the Nilpena Sandstone Member, D. costata is joined by Dickinsonia rex Jenkins 1992, which appears to be confined to the member, and is here re-described to clarify its taxonomic status and stratigraphic distribution.
ResearchGate has not been able to resolve any references for this publication.